

 
 

 
 

 
Lens/
optics
Lens/
optics
2
Simulation Simulation 2
 
      . 
     
         . 
     .
        
      .
      .
 -
 
 
 
 

 -

 
  7.3  7.3   
   .  1  S1
    2  S2  .
 
S1 A
R1
C1
S2
R2
S2
B
1
2
O
  
S1 B
R1
C1
S2
R2
S2
D
1
2
O
C2
C
A
  
 (Centre of curvature : C)    
  ,      . 
 C1 C2    .
  (Radius of curvature : R)   
    
  (R1R2)    .
 (Principal axis)      
    .
 (Optical centre : O)
         
    .   O
   P1Q1, P2 Q2     O
  .
( 7.4)
7.4  
P 1
P 3
P 2
Q 1
Q 2
Q 3
Biconvex
Converging Lens Diverging Lens
P 1
P 3
P 2
Q 1
Q 2
Q 3
Biconvex
  (Principal focus : F)    
        
     .   
  . F1 F2   .
  7.5     
       
(  )     (Converging lense)
.
 
(Converging
lense)
  7.5
       
         
        . 7.5 
     . F1 F2   
.
  7.5     
    
   ( ),   
 (Diverging lense) 
  7.5 b
 (Diverging lense)
Converging Lens
Focal Point
Focal length, f
NOTE: Focal length is defined for
initially parallel rays.
  
Converging Lens Diverging Lens
Double-convex Double-concave
Real focus
Virtual
focus
  
Converging Lens Diverging Lens
f
+
f
-
  f    () 
      .
Focal length f
FF
  7.5 b
 (Diverging lense)
Diverging Lens
Virtual Focal
Point
Negative Focal
length, -f
Rays appear to emerge from
Virtual Focal Point
   :
       
    .   
      .  
    ,   
  .     
        
.
   :
 1 :        
   .
 2 :         
   .
 3 :         
   .
 
Ray Diagrams for Converging Lenses
Ray 1 is parallel to the axis and refracts through F.
Ray 2 passes through Fbefore refracting parallel to the axis.
Ray 3 passes straight through the center of the lens.
The image is real and inverted. In this case, it is larger than
the object.
OFF
I
  7.7   AB   2F1  
. B        BC
   F2  CT    B  
   
 BO     OS    CT 
 Bl   Bl B     .
  7.7
        
.    .
1.         
    .
2.          
  .
   
Ray Diagrams for Diverging Lenses
Ray 1 is parallel to the axis and refracts as if from F.
Ray 2 heads towards Fbefore refracting parallel to the axis.
Ray 3 passes straight through the center of the lens.
The image is virtual and upright. It is smaller than the object.
OF FI
  7.9   PQ   F12F1  
 . P      PA
   AD   . AD  
   F1    .P 
  O    PO 
     . PO   AF1  
  P1    P    P1
 . Q       P  
  Q1  .  PQ  
 P1 Q1  .
         ,
     .
  (u)   (v)     (f) 
    .    .
   
     
.    
   .
 (Lens formula)
  ,   (O)    .
  (Frame of Referance) X  .  
 .
1.     .    
   .
2.          
   .
3.       ( ) 
.
4.       ( ) 
.
5.             
.
   (Power of a lens)
         
    (P)  .
         .   
           
.      (D) .
  (Combination of lenses)
   f1 f2    
      f     .
P1 P2           
(P)       
        . P = P1+ P2
    
(Human eye and working of its lens)
     
.    (  7.11
).      .
    
    . 
     .
 .  
  . 
      
    .
     
   .
ANATOMY OF THE EYE Superior Rectus Muscle
Iris
Anterior
chamber
Cornea
Pupil
Lens
Ciliary Body
and Muscle
Inferior Rectus Muscle
Vitreous Gel (body)
Choroid
Optic Nerve
Macula
Fovea
Retina


       
    
.   
  .  
    
 .  . 
     .
    
     .
    
(Human eye and working of its lens)
    
(Human eye and working of its lens)
  ()     . 
        
   .   
   .    
       ,   
  .
     (Human eye and working of its lens)
 ( )    
      . (  7.12  ) 
       
    . (  7.12 )  
      .
      
    .   
        
       
.
        
        
       
 .     
25 cm  .      
        
       
.       .
   2.4 cm . 
    .
     
    .
 
   
    2 cm . 
 
      .
   (Defects of vision and their
corrections)
        
  .    
 . :     .
1.      (Nearsightedness/ Myopia)
         
   ,     
    .   ,  
     (  7.13 ).
      .
 
1.         
   .
2.       
 .
1.     
(Nearsightedness/ Myopia)
 -       
     .    
      .  
        .
      .  
     .  
       .
1.   
 
(Nearsightedness/
Myopia)
1.     
(Nearsightedness/ Myopia)
2.  (Farsightedness/Hypermetropia)
         
     ,   
25cm   .    
   . (  7.14 ) 
  .
2.  (Farsightedness/Hypermetropia)
2.  (Farsightedness/Hypermetropia)
 
1.        
     .
2.       
  
2.  (Farsightedness/Hypermetropia)
 -         
  .         
       
     .    
  ,      
 .     
    .
2.  (Farsightedness/Hypermetropia)
3.  (Presbyopia)
      :  .
       
 .      
      
  .      
  .     -  
  -      
        
  .
    (Apparant size of
object)
   
     
  PQ P1Q1. PQ 
    (α) 
P1 Q1      (β)
   
  PQ  P1
Q1  .  
      
    

   (Use of concave lenses)
.  ,   ..  :  
    .    
      .
.       , 
      
  .        
 .
.  :     
    
.  :     
     .
. ,   :  
    .  
       
       .
   (Use of convex lenses)
.   (Simple Microscope)
        
,     
 .    .
   (magnifying glass)  .
    20    
.   ,   
     .
      . 
 ,   ,  
      
.     .
       
 .        
 .         
    .   
    .
.  (Compound Microscope)
      
     . ,
       
 .    .
1.   -   .
2.   -      .
        
      .    
     ,    
    .
.     (Telescope)
         
.       
,     .    
 .     
       
  .
.  
   ,  ,   
  .
. 
      
 .
          
.   
     .   
 .  
,       
.  
  ,    .  
   
  ?
 (Persistance of vision)
       . 
    .    
        
,        
    .  
        .
    ,   
  .      
.
 
.         
.  ,    
       
        .
    .    
      .   
         . 
  (Colour blind) .  
    .
Drawing a Concave Lens Ray Diagram
S
: Smaller
A
: Upright
L
: In front of F
T
: Virtual
2F F F’’ 2F
Step 1
Draw a ray parallel to the
principal axis that is refracted
through the principal focus (F).
Step 2 Draw a ray that passes
through the secondary
principal focus (F') and
refracts parallel to the
principal axis.
Step 3 Draw a ray that passes
through the optical center
goes straight through,
without bending.
Drawing a Concave Lens Ray Diagram
S
: Smaller
A
: Upright
L
: In front of F
T
: Virtual
2F F F’’ 2F
Step 1
Draw a ray parallel to the
principal axis that is refracted
through the principal focus (F).
Step 2 Draw a ray that passes
through the secondary
principal focus (F') and
refracts parallel to the
principal axis.
Step 3 Draw a ray that passes
through the optical center
goes straight through,
without bending.